Subsea wellbore operations vessel

ABSTRACT

A vessel adapted to perform subsea wellbore related operations involving a riser string between the subsea wellbore and the vessel. The vessel includes a hull having a deck, and a riser storage hold present within said hull below said deck. The riser storage hold comprising storage racks adapted to store therein parallel stacks of multiple riser sections and/or pre-assembled riser stands in a horizontal orientation. The vessel has an elongated riser transfer opening between said deck and said roof, and the riser transfer opening extending in a direction parallel to said storage racks. The vessel has horizontal rails extending along said opposite longitudinal sides of said riser transfer opening and a catwalk machine having a mobile catwalk machine frame that is movable over said horizontal rails. The catwalk machine is at least in a loading position that is above said riser transfer opening and in a riser upending position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of co-pending U.S. patent applicationSer. No. 15/517,841 filed on Apr. 7, 2017, which is the National Phaseof PCT International Application No. PCT/EP2015/073410 filed on Oct. 9,2015, which claims the priority benefit under 35 U.S.C. § 119(a) toNetherlands Patent Application No. 2013614 filed on Oct. 10, 2014, allof which are hereby expressly incorporated by reference into the presentapplication.

FIELD OF THE INVENTION

The present invention relates to a vessel adapted to perform subseawellbore related operations involving a riser string between the subseawellbore and the vessel, e.g. drilling and/or wellbore intervention.

The present invention also relates to a riser string extending between avessel and a subsea wellbore.

BACKGROUND OF THE INVENTION

In the prior art it is common to store the multiple riser sections fromwhich the subsea riser string is composed in a riser storage of thevessel.

Commonly a riser section comprises a riser pipe and in many knownembodiments additionally one or more satellite or peripheral pipes onthe outside of and along the riser pipe. The satellite pipes are e.g.used as fluid lines to a BOP or other subsea equipment, e.g. chokelines, kill lines, hydraulic lines, booster lines, injection lines (e.g.for glycol), etc. Each riser section comprises a connector fittingarrangement at each end thereof. For example the connector fittingarrangement includes a flange having bolt holes, with riser sectionsbeing joined by interconnecting flanges by means of bolts and nuts. Asatellite pipe may have an individual connector fitting, e.g. a bayonetfitting, or be designed to fit sealingly into the satellite pipe of anadjoining riser section without direct axial securing of the satellitepipes. In many practical embodiments a riser section is provided withone or more buoyancy and/or thermal insulation members, e.g. of foammaterial, but so-called bare joints are also employed.

Riser sections come in different lengths. Commonly riser sections havelengths between 50 ft. (15.24 meters) and 90 ft. (27.43 meters). A verycommon length for riser sections is 75 ft. (22.86 meters).

Riser sections are commonly heavy; far heavier than other tubulars usedin the offshore drilling industry. For example a single 75 ft. subseariser section may weigh between 20 and 25 tonnes, which is incomparableto the weight of an equally long drill pipe. Therefore riser handling issubject to different considerations than drill pipe handling, mainly inview of their size (diameter) and weight.

For example WO2009/102196 discloses a mono-hull vessel having a hull anda riser storage hold within the hull. In the riser storage hull risersections are stacked in their horizontal orientation. A gantry crane isprovided to raise and lower the riser sections out of and into thestorage hold and to place each individual riser section onto a risercatwalk machine or to pick up a riser section from the catwalk machine.The leading end of the riser section is in practice connected to a riserstring lifting tool which connects the riser section to a riser stringhandling capacity hoisting device of the vessel. By raising the liftingtool and operation of the catwalk machine the riser section is broughtinto a vertical orientation, or upended, in line with a firing linealong which the riser string is suspended into the sea. The alreadylaunched portion of the riser string is then temporarily held by a riserstring hanger, often referred to as a riser spider, of the vessel. Thenew riser section is then held in alignment above the launched riserstring and the connector fitting arrangements are interconnected to jointhe new riser section to the riser string. Then the riser string isreleased by the riser string hanger and lowered over the length of thenewly attached section. The riser string is then suspended again fromthe riser string hanger and the process of joining a new riser sectionis repeated.

It has been found that this known process to assembly a riser string istime-consuming. In particular a great deal of effort has to be made toproperly make up the connections between the connector fittingarrangements of the riser sections. In particular in view of desired orrequired testing of each connection that has been made up the knownprocess is undesirably slow.

OBJECTS OF THE INVENTION

The present invention aims to propose measures that allow forimprovements over the known approach, in view of pace with which theriser string can be assembled and/or disassembled, as well as in view ofthe actual storing and/or handling of riser sections on board a vessel.

SUMMARY OF THE INVENTION

A first aspect of the present invention relates to a vessel adapted toperform subsea wellbore related operations involving a riser stringbetween the subsea wellbore and the vessel, e.g. drilling and/orwellbore intervention. The vessel comprises a hull having a deck. Ariser storage hold is present within the hull below the deck. The riserstorage hold comprises storage racks adapted to store therein parallelstacks of multiple riser sections and/or pre-assembled riser stands in ahorizontal orientation. The riser storage hold has a floor, side walls,and a roof.

The vessel has an elongated riser transfer opening between the deck andthe roof. The riser transfer opening extends in a direction parallel tothe storage racks and has opposite longitudinal sides, a length, and awidth so as to allow for transfer of a single riser section or a singleriser stand in a horizontal orientation thereof via the riser transferopening out of and into the riser storage hold.

A riser transfer station is arranged within the riser storage hold belowthe riser transfer opening and is provided with a transfer elevator thatis adapted to raise and lower a single riser section or a single riserstand in the horizontal orientation thereof so as to pass the risersection or the riser stand through the riser transfer opening.

Horizontal rails extend along the opposite longitudinal sides of theriser transfer opening.

The vessel comprises a catwalk machine having a mobile catwalk machineframe that is movable over these horizontal rails. The catwalk machineframe has a rear end and a front end. The catwalk machine frame ismovable over the horizontal rails at least in a loading position that isabove said riser transfer opening and in a riser upending position.

The catwalk machine frame has two parallel and horizontal frame beams. Askate is supported by these frame beams and is configured to travel overthese frame beams. The skate comprises a riser end support that isconfigured to support thereon a rearward end of a riser section or of ariser stand.

The catwalk machine frame comprises, in addition to the riser endsupport, one or more additional riser support members that are eachmovable between an inactive position and an active position, wherein ariser section or riser stand is supportable on the riser end support andthe one or more additional riser support members when in the activeposition thereof.

The horizontal frame beams of the catwalk machine frame define betweenthem an opening that is dimensioned so that, with the catwalk machineframe in the loading position thereof and with the one or moreadditional riser support members in the inactive position thereof, asingle riser section or a single riser stand in the horizontalorientation thereof is lowerable through this opening between thehorizontal frame beams and into the riser transfer opening or isliftable out of the riser transfer opening and through this openingbetween the horizontal frame beams.

In an embodiment the horizontal frame beams are rigidly interconnectedby a transverse beam near said rear end of the catwalk machine frame,wherein the horizontal frame beams are further interconnected by one ormore mobile transverse connectors that are each movable between aninactive position. Herein a single riser section or a single riser standin said horizontal orientation thereof is lowerable through this openingbetween the horizontal frame beams and into the riser transfer openingor is liftable out of the riser transfer opening and through the openingbetween the horizontal frame beams, and an active position wherein theone or more mobile transverse connector interconnect the horizontalframe beams.

In an embodiment the horizontal frame beams are rigidly interconnectedby a transverse beam near the rear end of the catwalk machine frame, andthe horizontal frame beams are further interconnected by a single mobiletransverse connector arranged at the front end of the catwalk machineframe. Herein the single mobile transverse connector is movable betweenan inactive position, wherein a single riser section or a single riserstand in the horizontal orientation thereof is lowerable through theopening between the horizontal frame beams and into the riser transferopening or is liftable out of the riser transfer opening and through theopening between the horizontal frame beams, and an active positionwherein the single mobile transverse connector interconnects thehorizontal frame beams.

In an embodiment the vessel is provided with one or more movable hatcheswhich in a closed position thereof close the elongated riser transferopening and in an opened position thereof open the elongated risertransfer opening.

In an embodiment the vessel is provided with a first set of pivotalhatches, the first set of pivotal hatches being arranged along one ofthe longitudinal sides of the riser transfer opening. Herein the vesselis provided with a second set of pivotal hatches, the second set ofpivotal hatches being arranged along the other one of the longitudinalsides of the riser transfer opening, so that with these pivotal hatchesin a horizontal position thereof, the riser transfer opening is closedand with these hatches in an upward pivoted position thereof the risertransfer opening is open. In the upward pivoted position thereof, thepivotal hatches are to the outside of the horizontal rails at a spacingthat allows for travel of the catwalk machine frame over the horizontalrails between the upwardly pivoted hatches.

In an embodiment the vessel has a moonpool that extends through thehull, wherein the vessel is provided with a tower arranged at themoonpool and with a riser string lifting tool that is movable up anddown relative to the tower. Herein the riser string lifting tool isadapted to connect to a leading of a riser section or riser standsupported on the catwalk machine in the riser upending position of thecatwalk machine frame, the riser sting lifting tool further beingadapted to support a riser string in a firing line through the moonpool.

In an embodiment a first overhead travelling beam crane is arrangedwithin the riser storage hold, this first crane being adapted to liftand lower a single riser section or a single riser stand at leastallowing for removal of a single riser section or a single riser standriser stand from a storage rack and for placing a single riser sectionor a single riser stand into a storage rack respectively, and said firstcrane being adapted for transverse transportation of a single risersection or a single riser stand at least between said transfer stationand a position above a storage rack. Herein the first crane comprises:

-   -   a travelling beam extending in a direction parallel to said        storage racks and supported at each end thereof on a crane rail        perpendicular to said storage racks,    -   a winch trolley provided with one or more winches and        displaceable along said travelling beam,    -   an elongated gripper frame suspended by one or more winch driven        cables from said winch trolley, said gripper frame being        provided with multiple riser grippers adapted to engage on a        single riser section or a single riser stand at spaced gripping        locations thereof.

Herein the riser storage hold is provided with first length storageracks adapted to store therein single first length riser sections and/orpre-assembled riser stands, each of said single first length risersections or of pre-assembled riser stands having a length of at least100 ft. (30.48 m), e.g. of 120 ft. (36.57 m) or 150 ft. (45.72 m). Alsothe riser storage hold is provided with second length storage racksadapted to store therein single second length riser sections each havinga length of between 50 ft. (15.24 meters) and 90 ft. (27.43 meters),e.g. of 75 ft. (22.86 meters).

The first overhead travelling beam crane is adapted to transfer a secondlength riser section between each of said second length storage racks(90) and the transfer station, and to transfer a first length risersection or riser stand between each of said first length storage racksand the transfer station.

Due to the presence of both first length storage racks as well as secondlength storage racks the vessel can store both single first length risersections and/or pre-assembled riser stands (62) each having a length ofat least 100 ft. (30.48 m), e.g. of 120 ft. (36.57 m) or 150 ft. (45.72m), and single second length riser sections each having a length ofbetween 50 ft. (15.24 meters) and 90 ft. (27.43 meters), e.g. of 75 ft.(22.86 meters). In a very practical embodiment there are storage racksdedicated to 150 ft. (45.72 m) riser sections and/or pre-assembled riserstands and storage racks dedicated to 75 ft. (22.86 meters) risersections.

The riser storage may include at opposed ends of the space for storageof pre-assembled riser stands a platform assembly with personnelaccessible platforms at multiple levels so as to allow access ofpersonnel to the connector fitting arrangements at the ends of the riserstands.

For example the riser transfer opening has a width between 1.5 and 4.0meters.

The riser transfer opening will have a length at least equal to firstlength riser section or stand, e.g. a length of about 50 meters for thepassage of 150 ft. (45.72 m) riser sections and/or pre-assembled riserstands.

The first, possibly only, overhead travelling beam crane is adapted totransfer a second length riser section between each of the second lengthstorage racks and the transfer station, and to transfer a first lengthriser section or riser stand between each of the first length storageracks and the transfer station.

In a preferred embodiment two second length storage racks are arrangedin line with one another, parallel to the first length storage racks.This allows for efficient use of the volume within the hull of thevessel and efficient access to said second length storage racks by theoverhead crane.

In an embodiment the vessel has stored both first length riser sectionsand/or pre-assembled riser stands each having a length of at least 100ft. (30.48 m), e.g. of 120 ft. (36.57 m) or 150 ft. (45.72 m), andsecond length single riser sections each having a length of between 50ft. (15.24 meters) and 90 ft. (27.43 meters), e.g. of 75 ft. (22.86meters).

For example, and as preferred, each riser stand consists of two risersections, preferably equally long single riser sections. Each singleriser section comprises a riser pipe and optionally one or moresatellite pipes on the outside of and along the riser pipe. Each risersection comprises a connector fitting arrangement at each end thereof.Preferably each riser section comprises one or more buoyancy members.

Through the use of first length riser sections or pre-assembled riserstands stored in the riser storage the time needed for deployment and/orretrieval of a riser string is reduced compared to the present practicewherein second length riser sections are interconnected in the firingline. The use of first length riser sections or pre-assembled riserstands for example allows to bring up the blow-out preventer or a modulethereof attached to the lower end of the riser string without causingundue delay of the drilling process. The blow out preventer or modulethereof can then, e.g., be subject to inspection and/or maintenance,which enhances safety of subsea drilling, e.g. in great water depths.Also great progress is made in the deployment process in view ofrepetitive testing of the leak tightness of the riser string, which iscommonly done after three new riser sections have been added to thestring. With the use of first length riser sections or pre-assembledriser stands a significant reduction of the number of pressure tests maybe required, or testing may be done with less time pressure per test tobe performed.

In order to benefit optimally from the invention it is envisaged thatthe main storage of riser sections onboard the vessel is embodied asstorage for first length riser sections or pre-assembled riser stands,so that a majority, e.g. at least 60%, of the riser string length thatis stored onboard the vessel, is stored as these first length risersections or riser stands. For example the storage racks are embodied tostore therein at least 6000 ft. in total of first length riser sectionsor stands, e.g. at least 40 riser sections or stands of 150 ft. each.

The storage racks may also be embodied to store therein at least 1500ft. in total of second length riser sections, e.g. at least 20 risersections of 75 ft. each.

Possibly also some so-called pup sections of very limited length thatare commonly employed in the industry can be stored onboard, e.g. withinthe riser storage hold.

Further riser string items like a telescopic joint, hang-off joint, etc.can also be stored onboard the vessel.

It is noted that in non-prepublished PCT/NL2014/050201 a vessel isdisclosed having a riser storage hold within the hull below the deck.The riser storage hold comprises storage racks adapted to store thereinparallel stacks of multiple riser sections and/or pre-assembled riserstands in horizontal orientation. The vessel is provided with anelongated riser transfer opening between the deck and the roof of thestorage hold. This riser transfer opening extends in a directionparallel to the storage racks and has a length and a width so as toallow for transfer of a single riser section or a single riser stand inhorizontal orientation via the riser transfer opening out of and intothe riser storage hold. The vessel is further provided with a risertransfer station arranged within the riser storage hold below the risertransfer opening. This station is provided with a transfer elevator thatis adapted to raise and lower a single riser section or a single riserstand in horizontal orientation thereof so as to pass the riser sectionor a riser stand through the riser transfer opening. Within the riserstorage hold an overhead travelling beam crane is arranged, which craneis adapted to lift and lower a single riser section or a single riserstand at least allowing for removal of a single riser section or asingle riser stand riser stand from a storage rack and for placing asingle riser section or a single riser stand into a storage rackrespectively. The crane is also adapted for transverse transportation ofa single riser section or a single riser stand at least between thetransfer station and a position above a storage rack.

In an embodiment the transfer elevator comprises a first elevator unitand a second elevator unit, which units are spaced apart in a directionparallel to the storage racks. Each of the first and second elevatorunits are adapted to selectively operate stand-alone or in unison. Whenoperating in stand-alone mode each elevator unit is used to raise andlower a second length riser section, e.g. a 75 ft. (22.86 meters) risersection. When operating in unison the first and second elevator unitsare used to raise and lower a first length riser section or single firstlength riser stand, e.g. a 150 ft. (45.72 m) riser section and/orpre-assembled riser stand.

Each elevator unit, in an embodiment, comprises a vertical guidestructure, preferably stationary mounted in the storage hold, and atelescoping member which is guided by the vertical guide structure. Ariser support member is mounted on the telescoping member and is adaptedto support a riser section or riser stand thereon.

In an embodiment the elevator unit further comprises a winch and winchdriven cable connected to the telescoping member to cause verticalmotion thereof. For example, in view of redundant construction, twowinches may operate a single winch driven cable, e.g. each winchattached to a different cable end, so that operations can continue incase of winch failure. In an alternative one can envisage arack-and-pinion drive for the telescoping member or e.g. one or morehydraulic cylinders.

In an embodiment a riser support member is a riser support table havinga length of between 20 and 50 ft. The significant length may allow toengage the riser support table directly with one or more buoyancymembers fitted on the riser section or riser stand as the load is thendistributed over a significant area.

In an embodiment the riser support member is pivotally connected to thetelescoping member and tiltable between a horizontal operation positionwherein a riser section or riser stand can rest on said riser supportmember and a vertical inoperative storage position.

In an embodiment a first group of first length storage racks is arrangedadjacent one side of the transfer station and a second group of firstlength storage racks is arranged adjacent another side of the transferstation. This allows for a relative short distance of travel of thefirst length riser sections or stand between their respective storagerack and the transfer station. This enhances operating speed whenhandling the long and heavy first length riser sections and/or stands.

In an embodiment a first group of second length storage racks isarranged along the first group of first length storage racks and asecond group of second length storage racks is arranged along the secondgroup of first length storage racks.

In an embodiment a group of second length storage racks is arrangedalong a port side of the hold and another group of second length storageracks along a starboard side of the hold. One or more groups of firstlength storage racks are then arranged between said port and starboardside groups of second length storage racks. This means that the longestriser sections or stands are arranged more in the center of the hold,with the shorter second length riser section along the port andstarboard sides of the hold. This e.g. is favourable in view of thehandling of the longest first length riser sections or stand, e.g. whena transfer opening through deck is arranged centrally on the vessel.

As will explained below, in an embodiment, it is envisaged that therelative shorter, nowadays common, second length riser sections will beprovided with buoyancy members that are to be fitted in a lower part ofthe riser string, so with buoyancy members that have a high depthrating. Commonly buoyancy members have increasing specific weight andoverall mass as the depth rating increases in view of the water pressureto which the buoyancy member is subjected which increases with waterdepth. It is envisaged that fitting first length riser sections or firstlength riser stands stored in the storage with high depth ratingbuoyancy members would result in a total weight of each riser section orriser stand that renders the handling thereof very difficult, e.g. inview of sagging when held horizontally when conveyed by an overhead beamcrane. Therefore, in an embodiment, it is envisaged that multiple firstlength riser sections or riser stands and multiple second length risersections are each provided with buoyancy modules, wherein the buoyancymodules of the second length riser sections have a greater depth ratingthan the buoyancy modules of the first length riser sections. So theshorter elements have the relatively heavy buoyancy members and thelonger elements of the riser string have the relative light buoyancymembers, so that handling of both can be done effectively.

The present invention also envisages a riser string extending between asubsea wellbore and a subsea wellbore operations vessel, wherein theriser string comprises a lower string part composed of interconnectedsecond length riser sections and an upper string part composed ofinterconnected first length riser sections or riser stand, wherein saidfirst length riser sections or riser stand and said second length risersections are each provided with buoyancy modules, and wherein thebuoyancy modules of the second length riser sections having a greaterdepth rating than the buoyancy modules of the first length risersections. It will be appreciated that such riser string can be assembledeffectively when using a vessel as described herein.

In an embodiment each storage rack comprises at ends thereof a pair ofadjacent riser end support columns that form a vertical slot which isadapted to receive therein an end portion, e.g. a flange, of a risersection or riser stand.

In an embodiment the riser storage hold is provided with at least oneelongated riser workshop having a floor, preferably also walls and apossibly also a roof.

The riser workshop is arranged parallel to the storage racks and theworkshop is adapted to accommodate at least one riser section or riserstand in horizontal orientation, preferably at least one first lengthriser section or riser stand, e.g. a 150 ft. length.

The workshop provides a space, preferably an enclosure, for personnelperforming work on the riser, e.g. maintenance and/or inspection of theriser and/or assembly of two riser sections to form a pre-assembledriser stand.

In an embodiment the first overhead travelling beam crane is adapted toplace a riser in the workshop and remove a riser from the workshop, e.g.the workshop having a roof with a riser transfer opening therein,preferably said opening being provided with a mobile roof cover, e.g.one or more hatches or a tarpaulin.

In a further embodiment a first elongated riser workshop and a secondelongated riser workshop are arranged in the riser storage hold, alongopposite sides of the storage racks, preferably with the transferstation centrally between storage racks. The arrangement of riserworkshops to the sides of the storage racks, e.g. along port andstarboard side of the hull in a monohull vessel, allows for effectiveuse of space, reduced crane handling distances, and enhances access tothe workshops for personnel.

In an embodiment the riser storage hold is provided, in addition to thefirst overhead travelling beam crane, with a second overhead travellingbeam crane arranged within the riser storage hold. This second crane isalso adapted to lift and lower a single riser section or a single riserstand at least allowing for removal of a single riser section or asingle riser stand riser stand from a storage rack and for placing asingle riser section or a single riser stand into a storage rackrespectively. The second crane is also adapted for transversetransportation of a single riser section or a single riser stand atleast between said transfer elevator and a position above a storagerack. The second crane comprises:

-   -   a second travelling beam extending in a direction parallel to        said storage racks and supported at each end thereof on a crane        rail perpendicular to said storage racks, preferably the same        crane rail as the first overhead travelling beam crane,    -   a second winch trolley provided with one or more winches and        displaceable along said travelling beam,    -   possibly, an elongated gripper frame suspended by one or more        winch driven cables from said winch trolley, said gripper frame        being provided with multiple riser grippers adapted to engage on        a single riser section or a single riser stand at spaced        gripping locations thereof.

The provision of the second crane creates a redundant crane system,which can continue to operate should the first crane have a failure. Onecan envisage that the gripper frame is then fitted onto the secondcrane, but also each crane can have its own gripper frame to allow for arapid changeover to the other crane. The provision of the second craneis in particular advantageous when a first elongated riser workshop anda second elongated riser workshop are arranged in the riser storagehold, at least one of said riser workshop being arranged along a side ofthe riser storage hold, and when the second travelling beam crane has aparking position above said workshop along the side of the riser storagehold. Most preferred is an embodiment wherein the other workshop isalong the opposite side of the riser storage hold so that the crane thatis not in use is parked at the side of the hold above the workshop withthe other workshop still accessible by means of the operational crane.

In an embodiment the vessel is provided with one or more movable hatcheswhich in a closed position thereof close the transfer opening and in anopened position thereof open the transfer opening, e.g. pivotal hatches.

In an embodiment the gripper frame is provided with two riser grippersthat are adapted and arranged to engage on the end portions of secondlength riser section, e.g. on end portions of a 75 ft. riser section.For example use is made of a riser gripper as disclosed in U.S. Pat. No.7,905,529. In another embodiment which is preferred, it is envisagedthat the riser grippers are each embodied to cooperate with a hook thatis fitted on the riser section or riser stand, e.g. a hook integratedwith a collar that is fitted around the riser pipe.

In an embodiment one or more, preferably all, of the first length risersections or riser stands are provided at intermediate locations alongthe length thereof with two riser gripper engageable portions, e.g. witha hook at each location, having a spacing the same as the spacingbetween end portions of a second length riser section so as to allow thetwo riser grippers to engage on these gripper engageable portions of thefirst length riser section or riser stand. So in an embodiment the risergrippers are arranged on the gripper frame to engage end portions, e.g.provided with hooks, of a 75 ft. riser section, with the vessel alsostoring 150 ft. riser sections or stand that are provided with twogripper engageable portions, e.g. hooks, at the same spacing or at leasta spacing that approximates said 75 ft. end portion spacing.

In an embodiment, in particular with the first length riser sectionhaving at intermediate locations along the length thereof with two risergripper engageable portions, the gripper frame is provided, at each endthereof, with a telescoping extender having an extender end, whichextender is extensible so that the extender end is adjacent the end of afirst length riser section or riser stand. The extender is preferablyused to cooperate with the storage racks to guarantee vertical guidanceof the gripper frame and riser section or stand held thereby duringlifting and lowering.

In an embodiment each first length storage rack comprises at endsthereof a pair of adjacent riser end support columns that form avertical slot which is adapted to receive therein an end portion, e.g. aflange, of a riser section or riser stand, and wherein the extender endis adapted to be slidingly received between these columns.

In an embodiment substantially horizontal rails extend along oppositelongitudinal sides of the riser transfer opening, and the vesselcomprises a riser horizontal transport device that is mounted on thesehorizontal rails and movable there along. The device is adapted toreceive and hold a riser section or riser stand that has been raisedthrough the transfer opening by the riser elevator and to horizontallytransport the riser section or riser stand so that a leading end thereofis connectable to a riser string lifting tool that is adapted to supportthe weight of a riser string in a firing line of the vessel.

In an embodiment the riser horizontal transport device comprises astrongback assembly as is disclosed in non-prepublishedPCT/NL2014/050201, which disclosure is incorporated herein by reference.

In another embodiment the riser horizontal transport device comprises acatwalk machine having a mobile catwalk machine frame that is movableover said horizontal rails, wherein the catwalk machine frame has a rearend and a front end, and is movable over the horizontal rails at leastin a loading position and in a riser upending position. The catwalkmachine frame has two parallel and horizontal frame beams, and a skateis supported by said frame beams and travels over the frame beams. Theskate comprises a riser end support to support thereon a rearward end ofa riser section or riser stand. The horizontal frame beams of thecatwalk machine frame define between them an opening having a width soas to allow for the vertical passing of a single riser section or asingle riser stand in horizontal orientation through said opening,preferably by means of the transfer elevator.

In addition to the skate the catwalk machine comprises one or moreadditional riser support members that are movable between an inactiveposition allowing for the mentioned vertical passage of the single risersection or single riser stand and an active position wherein the risersection or riser stand is supported on said riser support member.

The frame beams of the catwalk machine are rigidly interconnected by atransverse beam near the rear end of the catwalk machine frame, and theframe beams are interconnected by one or more mobile transverseconnectors that are each movable between an inactive position allowingfor said vertical passage of the single riser section or single riserstand and an active position wherein the transverse connectorinterconnects the frame beams, e.g. the catwalk machine frame having asingle transverse connector at the front end of the catwalk machineframe. The provision of one or more mobile transverse connectors allowsfor the length of the catwalk machine frame to be significantly lessthan the length of the transfer opening and less than the length of thefirst length riser section or riser stand as the first length elementcan pass in vertical direction, e.g. by means of the transfer elevator,when the connectors are in their inactive position.

In an embodiment the catwalk machine is provided with a tailing-in armdevice that is mounted at the forward end of the catwalk machine frame.For example one tailing-in arm is arranged on each main beam of theframe, with the arms being movable into an operative position to act inunison when tailing-in the riser section or stand during the last stageof the upending process. The mounting on the catwalk machine causes thetailing-in arm device to move along with the catwalk machine, and thusit forms no obstacle near the firing line when the catwalk machine isretracted, e.g. when not in use. In an alternative the tailing-in armdevice is supported on the vessel in a different manner, e.g. mobile inthe tower.

In an embodiment the vessel is provided with one or more movable hatcheswhich in a closed position thereof close the transfer opening and in anopened position thereof open the transfer opening, e.g. pivotal hatches.

In an embodiment a first set of pivotal hatches is arranged along onelongitudinal side of the transfer opening and a second set of pivotalhatches is arranged along the opposed longitudinal side of the transferopening, so that with said hatches in horizontal position the transferopening is closed and with said hatches in upward or downward pivotedposition the transfer opening is open.

In an embodiment with upwardly opening pivoting hatches for the transferopening it is envisaged that with said hatches in upward pivotedposition said hatches are to the outside of the horizontal rails at aspacing allowing for the travel of the catwalk machine over saidhorizontal rails between said upward pivoted hatches.

In an embodiment the vessel is a monohull vessel and the riser storageis embodied to store the riser section and/or riser stands thereinparallel to a longitudinal axis of the vessel.

In an embodiment the transfer opening is on the longitudinal midplane ofthe monohull vessel, preferably with the riser assembly firing line ofthe vessel also in said midplane.

In an embodiment the vessel has a moonpool and a tower is arranged atthe moonpool, e.g. at a side of the moonpool or above the moonpool, e.g.as in WO2009/102196.

In an embodiment the vessel is provided with a riser string hanger thatis adapted to suspended therefrom a riser string in a firing line intothe sea.

In an embodiment the vessel has a tower, e.g. at a moonpool or above amoonpool, with the riser string assembly firing line e.g. extendingthrough the moonpool, and a firing line hoisting device is provided, thehoisting device comprising a hanger device that is movable up and downrelative to the tower. Preferably the hanger device is embodied as atravelling hanger device that is movable up and down along one or morevertical rails mounted on the tower, e.g. a wheeled travelling hangerdevice having wheels engaging one or more vertical rails. Preferably thehoisting device comprises at least one winch and at least one cable,wherein the hanger device is suspended from the at least one cable.

In an embodiment the moonpool has lateral sides, a front side and a rearside, and the tower is embodied as a hollow construction mast having atop and having a base that is integral with the hull, the base extendingbetween sections of the hull on opposed lateral sides of the moonpool,the base being spaced from each of the front side and the rear side ofthe moonpool, thereby forming a front moonpool area forward of the mastand a rear moonpool area rearward of the mast, wherein the mast has afront side and an opposed rear side as well as opposed lateral sides. Atone of said moonpool areas, preferably the rear moonpool area, thevessel is provided with a riser string assembly hanger that is adaptedto suspended therefrom a riser string in a firing line into the seaduring the riser assembly and disassembly process.

In a preferred embodiment the vessel has a riser string handlingcapacity hoisting device including a riser string lifting tool which ismovable up and down relative to the mast and that is adapted to connectto an end of a riser section, preferably of a pre-assembled riser stand,and is embodied to support the weight of a riser string in the firingline when released from the riser string assembly hanger.

In a preferred embodiment the vessel has a second firing hoistingdevice, having a load attachment device which is movable up and downrelative to the mast at a side opposed from the riser firing line, so asto allow for handling of items passing through the other moonpool areaalong a second firing line distinct and spaced from the first firingline where the riser string assembly takes place. Preferably said secondhoisting device is embodied as a drilling drawworks, and is providedwith a topdrive suspended from the load attachment device to performdrilling operations.

Preferably the vessel has a moonpool and the vessel is provided with ariser string support cart that is displaceable within the moonpoolbetween the two firing lines allowing to assembly a riser string in ariser string assembly firing line, e.g. at the rear moonpool area, andthen to transfer the riser string to a drilling firing line, e.g. at afront moonpool area. For example this cart is embodied as a skid cartthat can be skidded over a pair of associated skid rails which extend inlongitudinal direction along the moonpool, allowing to displace the cartin longitudinal direction of the moonpool while supporting a riserstring (and preferably with a BOP attached to the lower end of the riserstring) lowered into the sea, generally between the one moonpool areaand the other moonpool area, so underneath the base of the mast.

In an embodiment the riser string support cart is also embodied tosupport a blow-out preventer or blow-out preventer module thereon, sowith the cart underneath the blow-out preventer or module thereof.

Preferably one or both of the riser string handling capacity hoistingdevices and—if present—the second firing line hoisting device comprisesone or more cables and one or more associated winches.

Preferably one or both of the riser string handling capacity hoistingdevices and—if present—the second firing hoisting device comprises aheave compensation mechanism.

It is envisaged that—if present—the riser transfer opening is orientedwith its length towards the moonpool, preferably along or parallel to acentral axis of the vessel if the vessel is a monohull vessel. E.g. thevessel has a riser storage hold aft of the moonpool.

In an embodiment the vessel has a moonpool. At the moonpool a tower,e.g. a hollow construction mast, is arranged. The vessel is providedwith a riser string hanger that is adapted to suspended therefrom ariser string in a firing line through the moonpool into the sea. Ahoisting device is provided having a hanger device that is movable upand down relative to the tower, e.g. the hanger device being suspendedfrom a cable connected to one or more winches.

A second aspect of the present application relates to a vessel adaptedto perform subsea wellbore related operations involving a riser stringbetween the subsea wellbore and the vessel, e.g. drilling and/orwellbore intervention, said vessel comprising a hull having a deck, saidvessel comprising:

-   -   a riser storage hold present within said hull below said deck,        which riser storage hold comprises storage racks adapted to        store therein parallel stacks of multiple riser sections and/or        pre-assembled riser stands in horizontal orientation,        which riser storage hold has a floor, side walls, and a roof,        wherein the riser storage hold is provided with first length        storage racks adapted to store therein single first length riser        section and/or pre-assembled riser stands (62) each having a        length of at least 100 ft. (30.48 m), e.g. of 120 ft. (36.57 m)        or 150 ft. (45.72 m),        and        wherein the riser storage hold is provided with second length        storage racks adapted to store therein single second length        riser sections each having a length of between 50 ft. (15.24        meters) and 90 ft. (27.43 meters), e.g. of 75 ft. (22.86        meters),        wherein two second length storage racks are arranged in line,        parallel to said first length storage racks.

The present invention also relates to a vessel adapted to perform subseawellbore related operations involving a riser string between the subseawellbore and the vessel, e.g. drilling and/or wellbore intervention,said vessel comprising a hull having a deck, said vessel comprising:

-   -   a riser storage hold present within said hull below said deck,        which riser storage hold comprises storage racks adapted to        store therein parallel stacks of multiple riser sections and/or        pre-assembled riser stands in horizontal orientation,        which riser storage hold has a floor, side walls, and a roof,    -   a first overhead travelling beam crane arranged within the riser        storage hold, said first crane being adapted to lift and lower a        single riser section or a single riser stand at least allowing        for removal of a single riser section or a single riser stand        riser stand from a storage rack and for placing a single riser        section or a single riser stand into a storage rack        respectively, and said crane being adapted for transverse        transportation of a single riser section or a single riser stand        at least between said transfer elevator and a position above a        storage rack,        wherein said first crane comprises:    -   a travelling beam extending in a direction parallel to said        storage racks and supported at each end thereof on a crane rail        perpendicular to said storage racks    -   a winch trolley provided with one or more winches and        displaceable along said travelling beam,    -   an elongated gripper frame suspended by one or more winch driven        cables from said winch trolley, said gripper frame being        provided with multiple riser grippers adapted to engage on a        single riser section or a single riser stand at spaced gripping        locations thereof,        and        wherein the riser storage hold is provided with a second        overhead travelling beam crane arranged within the riser storage        hold, said second crane being adapted to lift and lower a single        riser section or a single riser stand at least allowing for        removal of a single riser section or a single riser stand riser        stand from a storage rack and for placing a single riser section        or a single riser stand into a storage rack respectively, and        said second crane (50) being adapted for transverse        transportation of a single riser section or a single riser stand        at least between said transfer elevator and a position above a        storage rack,        wherein said second crane comprises:    -   a second travelling beam extending in a direction parallel to        said storage racks and supported at each end thereof on a crane        rail perpendicular to said storage racks, preferably the same        crane rail as the first overhead travelling beam crane,    -   a second winch trolley provided with one or more winches and        displaceable along said travelling beam,    -   possibly, an elongated gripper frame suspended by one or more        winch driven cables from said winch trolley, said gripper frame        being provided with multiple riser grippers adapted to engage on        a single riser section or a single riser stand at spaced        gripping locations thereof,

A third aspect of the present invention relates to a vessel adapted toperform subsea wellbore related operations involving a riser stringbetween the subsea wellbore and the vessel, e.g. drilling and/orwellbore intervention, said vessel comprising a hull having a deck, saidvessel comprising:

-   -   a riser storage hold present within said hull below said deck,        which riser storage hold comprises storage racks adapted to        store therein parallel stacks of multiple riser sections and/or        pre-assembled riser stands in horizontal orientation,        which riser storage hold has a floor, side walls, and a roof,    -   an elongated riser transfer opening between said deck and said        roof, said elongated riser transfer opening extending in a        direction parallel to said storage racks, and said elongated        riser transfer opening having a length and a width so as to        allow for transfer of a single riser section or a single riser        stand in horizontal orientation via said riser transfer opening        out of and into the riser storage hold,    -   a riser transfer station arranged within said riser storage hold        and provided with a transfer elevator that is adapted to raise        and lower a single riser section or a single riser stand in        horizontal orientation thereof so as to pass the single riser        section or a single riser stand through the riser transfer        opening,    -   a first crane arranged within the riser storage hold, said first        crane being adapted to lift and lower a single riser section or        a single riser stand at least allowing for removal of a single        riser section or a single riser stand riser stand from a storage        rack and for placing a single riser section or a single riser        stand into a storage rack respectively, and said first crane        being adapted for transverse transportation of a single riser        section or a single riser stand at least between said transfer        elevator and a position above a storage rack,        wherein the riser storage hold is adapted to store therein        single first length riser section and/or pre-assembled riser        stands (62) each having a length of at least 100 ft. (30.48 m),        e.g. of 120 ft. (36.57 m) or 150 ft. (45.72 m),        and        wherein the riser storage hold is adapted to store therein        single second length riser sections each having a length of        between 50 ft. (15.24 meters) and 90 ft. (27.43 meters), e.g. of        75 ft. (22.86 meters),        wherein the transfer elevator comprises a first elevator unit        and a second elevator unit that are spaced apart in a direction        parallel to said storage racks, wherein each of said first and        second elevator units are adapted to selectively operate        stand-alone or in unison, wherein, for operating stand-alone,        each elevator unit is adapted to raise and lower a second length        riser section, and wherein, for operating in unison, said first        and second elevator units are further adapted to raise and lower        a first length riser section or single riser stand.

A fourth aspect of the present invention relates to a vessel adapted toperform subsea wellbore related operations involving a riser stringbetween the subsea wellbore and the vessel, e.g. drilling and/orwellbore intervention, said vessel comprising a hull having a deck, saidvessel comprising:

-   -   a riser storage hold present within said hull below said deck,        which riser storage hold comprises storage racks adapted to        store therein parallel stacks of multiple riser sections and/or        pre-assembled riser stands in horizontal orientation,        which riser storage hold has a floor, side walls, and a roof,    -   an elongated riser transfer opening extending between said deck        and said roof, said elongated riser transfer opening being a        parallel to said storage racks, and said elongated riser        transfer opening having a length and a width so as to allow for        transfer of a single riser section or a single riser stand in        horizontal orientation via said riser transfer opening out of        and into the riser storage hold,    -   a riser transfer station arranged within said riser storage hold        and provided with a transfer elevator that is adapted to raise        and lower a single riser section or a single riser stand in        horizontal orientation thereof so as to pass the single riser        section or a single riser stand through the riser transfer        opening,        wherein a first elongated riser workshop and a second elongated        riser workshop are arranged in the riser storage hold, wherein        each riser workshop has a floor, preferably also walls and a        possibly also a roof,        the first and second workshop each being arranged along a side        of the storage hold, the storage racks being positioned between        said first and second workshops,        wherein each riser workshop is arranged parallel to the storage        racks and the workshop is adapted to accommodate at least one        riser section or riser stand in horizontal orientation, the        workshop providing a space, preferably an enclosure, for        personnel performing work on the riser, e.g. maintenance and/or        inspection of the riser,        wherein the vessel comprises a crane is adapted to place a riser        in the workshop and remove a riser from the workshop, e.g. the        workshop having a roof with a riser transfer opening therein,        preferably said opening being provided with a mobile roof cover,        e.g. one or more hatches or a tarpaulin.        wherein, preferably, the transfer station is located centrally        between storage racks.

A fifth aspect of the present invention relates to a vessel adapted toperform subsea wellbore related operations involving a riser stringbetween the subsea wellbore and the vessel, e.g. drilling and/orwellbore intervention, said vessel comprising a hull having a deck, saidvessel comprising:

-   -   a riser storage,        which riser storage comprises storage racks adapted to store        therein parallel stacks of multiple riser sections and/or        pre-assembled riser stands in horizontal orientation,        wherein the riser storage is provided with first length storage        racks wherein single first length riser section and/or        pre-assembled riser stands (62) each having a length of at least        100 ft. (30.48 m), e.g. of 120 ft. (36.57 m) or 150 ft.        (45.72 m) are stored,        and        wherein the riser storage is provided with second length storage        racks wherein single second length riser sections each having a        length of between 50 ft. (15.24 meters) and 90 ft. (27.43        meters), e.g. of 75 ft. (22.86 meters) are stored,    -   a first overhead travelling beam crane adapted to lift and lower        a single riser section or a single riser stand at least allowing        for removal of a single riser section or a single riser stand        riser stand from a storage rack and for placing a single riser        section or a single riser stand into a storage rack        respectively, and said first crane being adapted for transverse        transportation of a single riser section or a single riser        stand,        wherein said first crane comprises:    -   a travelling beam extending in a direction parallel to said        storage racks and supported at each end thereof on a crane rail        perpendicular to said storage racks,    -   a winch trolley provided with one or more winches and        displaceable along said travelling beam,    -   an elongated gripper frame suspended by one or more winch driven        cables from said winch trolley, said gripper frame being        provided with two riser grippers,        wherein the first length riser sections or riser stands are each        provided at intermediate locations along the length thereof with        two riser gripper engageable portions having a spacing the same        as the spacing between end portions of a second length riser        section so as to allow said two riser grippers to engage on said        gripper engageable portions of the first length riser section or        riser stand.

A sixth aspect of the present invention relates to a single risersection having a length of at least 100 ft. (30.48 m), e.g. of 120 ft.(36.57 m) or 150 ft. (45.72 m), wherein the riser section is provided atintermediate locations along the length thereof with two riser gripperengageable portions having a spacing corresponding to the spacingbetween end portions of a 75 ft. (22.86 meters) riser section.

In an embodiment each gripper engageable portion comprises a hook memberfitted to the riser section or riser stand, e.g. a hook integrated witha collar that is fitted around the riser pipe.

A seventh aspect of the present invention relates to a set of multiplefirst length riser sections or pre-assembled riser stands and multiplesecond length riser sections which are each provided with buoyancymodules, e.g. stored horizontally onboard a vessel, e.g. a vessel asdisclosed herein, wherein the buoyancy modules of the second lengthriser sections having a greater depth rating than the buoyancy modulesof the first length riser sections.

An eights aspect of the present invention relates to a riser stringextending between a subsea wellbore and a subsea wellbore operationsvessel, wherein the riser string comprises a lower string part composedof interconnected second length riser sections and an upper string partcomposed of interconnected first length riser sections or riser stand,wherein said first length riser sections or riser stand and said secondlength riser sections are each provided with buoyancy modules, andwherein the buoyancy modules of the second length riser sections havinga greater depth rating than the buoyancy modules of the first lengthriser sections.

Each aspect of the present invention also relates to a method forassembly of a riser string, wherein use is made of a vessel and/or risersections and/or pre-assembled riser stands as disclosed herein.

The present invention also relates to a riser handling overheadtravelling beam crane as described herein. The present invention alsorelates to handling first and second length riser sections orpre-assembled riser stands as described herein using said overheadtravelling beam crane, e.g. within a riser storage hold of a vessel.

It will be appreciated that any feature described with reference of oneaspect of the invention, e.g. described as an optional or a requiredfeature with respect to the first aspect of the invention, may bereadily combined with one or more of the other aspects of the inventionas described herein.

The invention will now be explained with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows in longitudinal view a vessel according to the invention,

FIG. 2 shows a plan view of the aft part of the vessel of FIG. 1,

FIG. 3 shows schematically a step in a riser upending process of thevessel of FIG. 1,

FIG. 4 shows a transverse section of the vessel of FIG. 1 showing theriser storage hold, the riser transfer elevator, the overhead cranes,

FIG. 5 shows a horizontal section of the riser storage hold of thevessel of FIG. 1,

FIG. 6 shows on a larger scale a portion of FIG. 5,

FIG. 7a illustrates a transfer elevator unit holding a riser section inraised condition,

FIG. 7b illustrates the transfer elevator unit in inoperative condition,

FIG. 8 illustrates the use of two transfer elevator units in unison forhandling a first length riser section,

FIG. 9 shows a portion of FIG. 8 on a larger scale,

FIG. 10 illustrates the use of a single transfer elevator unit instand-alone mode for handling a second length riser section,

FIG. 11 illustrates the provision of a hook as gripper engageableportion on a first length riser section,

FIG. 12 illustrates the provision of a hook as gripper engageableportion at the end of a second length riser section,

FIG. 13 illustrates an overhead crane handling a first length risersection in the storage hold of the vessel of FIG. 1,

FIG. 14 shows the overhead crane of FIG. 13 from above,

FIG. 15a shows the winch trolley and gripper frame of the crane of FIG.13 when handling a second length riser section,

FIG. 15b shows the gripper frame of FIG. 15a from above,

FIG. 16a shows the winch trolley and gripper frame of the crane of FIG.13 when handling a first length riser section with the extenders inextended position,

FIG. 16b shows the gripper frame of FIG. 16a from above,

FIG. 17 illustrates the handling of second length riser sections in thestorage hold by means of the crane of FIG. 13, and

FIG. 18 illustrates the catwalk machine, transfer opening and associatedhatches of the vessel of FIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a mono-hull vessel 1 having a hull 2 with a bow 3, a stern4, and a moonpool 5 that extends through the hull 1.

The vessel 1 is adapted to perform subsea wellbore related operationsinvolving a riser string between the subsea wellbore and the vessel, inparticular drilling operations, e.g. for exploratory drilling. Thevessel can also perform other subsea wellbore related operations, e.g.wellbore intervention.

In this example, the vessel 1 has an accommodation topside 6 at the bow3, including crew quarters and a bridge.

The vessel 1 has an engine room 7, generally below the accommodationtopside, with exhausts 7 a extending at the rear of the topside 6, abovethe topside 6.

The moonpool 5 has, as is preferred, a rectangular shape with opposedlateral sides, a front side and a rear side.

A front main deck 8 extends between the moonpool 5 and the topsides.

A rear main deck 9 extends between the moonpool 5 and the stern of thevessel 4.

The vessel is equipped with a tower 10, which is, as is preferred,embodied as a hollow construction mast having a top 11 and having a base12 that is integral with the hull 2. The base 12 extends betweensections of the hull on opposed lateral sides of the moonpool 5 and thebase 12 is spaced from each of the front side and the rear side of themoonpool, thereby forming a front moonpool area 5 a forward of the mast10 and a rear moonpool area 5 b rearward of the mast 10.

The mast 10 has a front side and an opposed rear side 10 b as well asopposed lateral sides.

In this example, drill pipe racks, here embodied as carrousel type racks14, are located adjacent the lateral sides of the mast 10, as is knownin the art.

At the rear moonpool area, the vessel is provided with a working deck 15arranged above the rear moonpool area 5 b. As is preferred the workingdeck 15 is a mobile working deck, here liftable along the mast 10 tosuch a height that a blow-out preventer can be brought and heldunderneath the working deck 15 in raised position thereof at an elevatedposition relative to the mast 10. In a lowered, operative position, theworking deck 15 preferably, as here, is level with the adjacent maindeck area.

In view of assembly and disassembly of a riser string along a firingline 20 through the rear moonpool area 5 b the vessel is equipped with ariser string assembly hanger 17 that is adapted to suspended therefrom ariser string in the firing line 20 into the sea during the riserassembly and disassembly process. As preferred, this hanger 17 ismounted on the working deck 15, e.g. embodied as a riser spider, e.g.provided with a gimballing support so as to allow for angular variationbetween the riser string and the working deck, e.g. due to sea motion ofthe vessel.

The vessel 1 has a riser string handling capacity hoisting deviceincluding a riser string lifting tool 25 which is movable up and downrelative to the mast 10 and that is adapted to connect to an end of ariser section, preferably of a pre-assembled riser stand as will beexplained below, and is embodied to support the weight of a riser stringin the firing line 20 when released from the riser string assemblyhanger 17.

The riser string lifting tool 25 here is suspended from a travellinghanger device 26 that is movable up and down along the rear side of themast 10 along one or more vertical rails 27.

The hanger device 26 is suspended by one or more cables 28 from a sheavearrangement 29 at the top of the mast, which one or more cables 28 areconnected to one or more winches 29 a, e.g. arranged within the mast 10.

It is noted that the firing line 20 is outside of the rear side 10 b ofthe mast 10 so that the firing line 20 can be reached without hindrancein the process of upending a riser section or riser stand from the rearof the vessel.

In an alternative embodiment, the mast 10 is replaced by a derrick typetower having a latticed frame with corner posts that forms a frameextending over the moonpool. It is then envisaged that the riser storageis outside of the derrick type tower and the derrick is provided with aV-door or similar to allow passage of a riser section or riser standinto and out of the derrick.

The vessel also has a second hoisting device having a load attachmentdevice 30 which is movable up and down relative to the mast at a sideopposed from the riser firing line 20, so as to allow for handling ofitems passing through the other moonpool area along a second firing line21 distinct and spaced from the first firing line 20 where the riserstring assembly takes place.

The second firing line 21 extends through the front moonpool area 5 a.Along this firing line 21 primarily drilling operations are performed.

The second hoisting device is embodied as a drilling drawworks, and isprovided with a topdrive 31 suspended from the load attachment device 30to perform drilling operations. The load attachment device 30 ispreferably embodied similar as the travelling hanger device 26.

A working deck 32 is arranged above the moonpool area 5 a and mayinclude a rotary table, iron roughneck machine, etc.

The vessel 1 is thus capable of assembly of a riser string in firingline 20. For transfer of the riser string to the other firing line 21 ariser string support cart 35 is provided that is displaceable within themoonpool, e.g. skiddable over rails along the lateral sides of themoonpool 5.

The vessel has a riser storage hold 40, here as is preferred, within thehull 2 aft of the moonpool 5.

The riser storage hold 40 comprises storage racks adapted to storetherein parallel stacks of multiple riser sections and/or pre-assembledriser stands in horizontal orientation.

The riser storage hold is provided with first length storage racks 80adapted to store therein single first length riser sections 85 and/orpre-assembled riser stands each having a length of at least 100 ft.(30.48 m), e.g. of 120 ft. (36.57 m) or 150 ft. (45.72 m). In theexample depicted in the figures the first length is 150 ft.

The riser storage hold is provided with second length storage racks 90adapted to store therein single second length riser sections 95 eachhaving a length of between 50 ft. (15.24 meters) and 90 ft. (27.43meters), e.g. of 75 ft. (22.86 meters). In the example depicted in thefigures the second length is 75 ft.

The second length storage racks 90 are arranged in sets of two arranged,with the two racks 90 being in line with one another and parallel to theadjacent longer first length storage racks 80.

A first group of first length storage racks 80 is arranged adjacent oneside of the transfer station 50 and a second group of first lengthstorage racks 80 is arranged adjacent another side of the transferstation 50.

A first group of second length storage racks 90 is arranged along thefirst group of first length storage racks and a second group of secondlength storage racks 90 is arranged along said second group of firstlength storage racks.

Each storage rack 80, 90 comprises at ends thereof a pair of adjacentriser end support columns that form a vertical slot which is adapted toreceive therein an end portion, e.g. a flange, of a riser section 85,95.

The riser storage hold has a floor 40 a, port and starboard side walls40 b,c, and a roof 41.

An elongated riser transfer opening 45 is present between the deck 9 andthe roof 41.

The riser transfer opening 45 extends in a direction parallel to thestorage racks and has a length, here of at least 150 ft., and a width soas to allow for transfer of a single riser section or a single riserstand in horizontal orientation via the riser transfer opening out ofand into the riser storage hold.

Within the storage 40 a riser transfer station 50 is arranged below theriser transfer opening 45. The station is provided with a transferelevator that is adapted to raise and lower a single riser section or asingle riser stand in horizontal orientation thereof so as to pass theriser section or a riser stand through the riser transfer opening 45.

In the storage hold 40 a first overhead travelling beam crane 60 isarranged.

The crane 60 is capable of lifting and lowering a single riser section85,95, either of first length or of second length as described herein,as well as a single pre-assembled first length riser stand as describedherein, at least allowing for removal of a single riser section or asingle riser stand riser stand from a storage rack and for placing asingle riser section 85, 95 or a single riser stand into a storage rackrespectively. The crane 60 is also capable of transverse transportationof a single riser section 85, 95 or a single riser stand at leastbetween the transfer station 50 and a position above each of the storageracks 80, 90 in the storage 40.

The first crane 60 comprises:

-   -   a travelling beam 61 extending in a direction parallel to the        storage racks and supported at each end thereof on a crane rail        62, 63 perpendicular to the storage racks, here transverse to        the hull 2,    -   a winch trolley 65 provided with one or more winches 66, 67 and        displaceable along the travelling beam 61,    -   an elongated gripper frame 68 suspended by one or more winch        driven cables 69 a, 69 b from the winch trolley, 65. The gripper        frame 68 is provided with multiple riser grippers 70 a, b that        are each adapted to engage on a single riser section 85, 95 or a        single riser stand at spaced gripping locations thereof.

The gripper frame 68 is provided with two riser grippers 70 a, b thatare adapted and arranged to engage on the end portions of second lengthriser section 95, here on end portions of a 75 ft. riser section.

The first length riser sections 85 are provided at intermediatelocations along the length thereof with two riser gripper engageableportions, here hooks 140, having a spacing the same as the spacingbetween end portions of a second length riser section 95 so as to allowsaid two riser grippers 70 a, b to engage on said gripper engageableportions 140 of the first length riser section 85.

The gripper frame 68 is provided, at each end thereof, with atelescoping extender 68 a, b having an extender end. Each extender 68 a,b is extensible so that the extender end is adjacent the end of a firstlength riser section 85 or riser stand. The end is dimensioned to beslidable received between two columns of a storage rack in order toguide the gripper frame and riser during vertical travel.

The crane 60 is adapted to transfer a second length riser section 95between each of the second length storage racks 80 and the transferstation 50, and to transfer a first length riser section 85 or riserstand between each of the first length storage racks 90 and the transferstation 50.

The transfer elevator comprises a first elevator unit 55 and a secondelevator unit 55, as is preferred of the same design. These units 55 arespaced apart in direction parallel to the storage racks.

Each of the elevator units 55 is adapted to selectively operatestand-alone or in unison. In stand-alone mode each elevator unit 55 isadapted to raise and lower a second length riser section (FIG. 10). Whenoperating in unison the elevator units 55 raise and lower a first lengthriser section or single riser stand together (FIG. 8,9).

Each elevator unit 55 comprises a vertical guide structure 56,stationary mounted in the storage hold 40. Further a telescoping member57 is provided, which is guided by the vertical guide structure 56. Theelevator unit further comprises a winch 58 and winch driven cable 59connected to the telescoping member 57 to cause vertical motion thereof.A riser support member 55 a is mounted on the telescoping member 57 andis adapted to support a riser section 85, 95 or riser stand.

The riser support member is a riser support table 55 a having a lengthof between 20 and 50 ft.

The riser support member 55 a is pivotally connected to the telescopingmember 57 and is tiltable, her by hydraulic cylinder, between ahorizontal operation position wherein a riser section or riser stand canrest on said riser support member and a vertical inoperative storageposition (see FIGS. 7a, 7b ).

The riser storage hold 40 is provided with a first elongated riserworkshop 110 and a second elongated riser workshop 120, each having alength at least sufficient to receive therein a first length risersection or stand. Each riser workshop has a floor, and, as is preferredalso walls and a roof.

Each riser workshop 110, 120 is arranged parallel to the storage racksand the workshop is adapted to accommodate at least one riser section85, 95 or riser stand in horizontal orientation. The workshop providesan enclosure for personnel performing work on the riser section, e.g.maintenance and/or inspection of the riser section and/orinterconnecting sections to form a pre-assembled stand.

The overhead travelling beam crane 60 is adapted to place a risersection 85, 95 in each of the workshops 110, 120 and remove a risersection from the workshop. In this example it is envisaged that theworkshops 110, 120 have a roof with a riser transfer opening therein,preferably said opening being provided with a mobile roof cover, e.g.one or more hatches or a tarpaulin.

As can be seen the workshops 110, 120 are arranged along the port andstarboard sides of the hold 40, along opposite sides of the storageracks 80, 90. The transfer station 50 is arranged centrally betweenstorage racks 80, 90.

The riser storage hold is provided with a second overhead travellingbeam crane 60′ which is provided to obtain a redundant crane system forhandling riser sections 85, 95. The crane 60′ is preferably of the samedesign as the crane 60. The travelling beam of crane 60′ preferablytravels on the same crane rails 62, 63 as the first overhead travellingbeam crane 60.

The second travelling beam crane 60′ here has a parking position aboveone of the workshops, here at 120, which workshop 120 preferably islocated along a side of the riser storage hold.

FIG. 4 shows that a further parking position is available for the crane60 above the other workshop 110, e.g. allowing to park crane 60 therewhen servicing is required and crane 60′ then has full access to allriser sections stored in the storage racks.

The vessel is provided with movable hatches which in a closed positionthereof close the transfer opening 45 and in an opened position thereofopen the transfer opening. e.g. pivotal hatches 130 a, 130 b.

Substantially horizontal rails 150 extend along opposite longitudinalsides of the riser transfer opening 45.

The vessel comprises a riser horizontal transport device 200 that ismounted on horizontal rails 150 and is adapted to receive and hold ariser section 85, 95 or riser stand that has been raised through saidtransfer opening 45 by the riser elevator unit or units 55 and tohorizontally transport the riser section 85, 95 or riser stand so that aleading end thereof is connectable to a riser string lifting tool thatis adapted to support the weight of a riser string in the firing line 20of the vessel.

The riser horizontal transport device comprises a catwalk machine havinga mobile catwalk machine frame that is movable over the horizontal rails150. The catwalk machine frame has a rear end and a front end and ismovable over the horizontal rails 150 at least in a loading positiongenerally above the opening 45 and in a riser upending position closerto the firing line 20.

The catwalk machine frame has two parallel and horizontal frame beams201, 202. At the rear end the beams 201, 202 are rigidly and permanentlyinterconnected by a transverse beam 203. The beams 201, 202 are lesslong than the transfer opening 45 and the first length riser section orstand that is stored in the hold 40. In order to obtain a sturdy frameduring transportation of the riser section it is envisaged that, hereonly at the front end, the frame beams 201, 202 are interconnected by amobile transverse connector 204 that is movable between an inactiveposition allowing for vertical passage of the single riser section orsingle riser stand and an active position wherein the transverseconnector 204 interconnects the frame beams 201, 202. When lifting andlowering a section of first length the connector 204 is inactive oropened. A shorter second length may be handled with the connectorremaining closed as the opening in the frame of the machine is thenlarge enough.

A skate 205 is supported by the frame beams 201, 202 and travels overthe frame beams. As is known in the art the skate 205 comprises a riserend support to support thereon a rearward end of a riser section 85, 95or riser stand.

As will be appreciated the horizontal frame beams 201, 202 of thecatwalk machine frame define between them an opening having a width soas to allow for the vertical passing of a single riser section 85, 95(equipped with buoyancy members) or a single riser stand in horizontalorientation through said opening, preferably by means of the transferelevator unit or units 55.

The catwalk machine, in addition to the skate 205, comprises one or moreadditional riser support members 206 that are movable between aninactive position allowing for said vertical passage of the single risersection 85, 95 or single riser stand and an active position wherein theriser section or riser stand is supported on said riser support member206.

If desired the catwalk machine 200 is provided with a tailing-in armdevice, e.g. with one tailing arm fitted to the front end of each beam201, 202.

As can be seen in FIG. 18 a first set of pivotal hatches 130 a,b isarranged along one longitudinal side of the transfer opening 45 and asecond set of pivotal hatches 130 a, b is arranged along the opposedlongitudinal side of the transfer opening 45, so that with said hatches130 a, b in horizontal position the transfer opening 45 is closed andwith said hatches in upward pivoted position the transfer opening 45 isopen.

As can be seen—in upward pivoted position—these hatches 130 a, b are tothe outside of the horizontal rails 150 at a spacing allowing for thetravel of the catwalk machine 200 over said horizontal rails 150 betweensaid upward pivoted hatches.

What is claimed is:
 1. A vessel adapted to perform subsea wellborerelated operations involving a riser string between the subsea wellboreand the vessel, said vessel comprising: a hull having a deck; a riserstorage hold present within said hull below said deck, said riserstorage hold comprising storage racks adapted to store therein parallelstacks of multiple riser sections and/or pre-assembled riser stands in ahorizontal orientation, and said riser storage hold having a floor, sidewalls, and a roof; an elongated riser transfer opening between said deckand said roof, said riser transfer opening extending in a directionparallel to said storage racks, said riser transfer opening havingopposite longitudinal sides, a length, and a width so as to allow fortransfer of a single riser section or a single riser stand in horizontalorientation thereof via said riser transfer opening out of and into theriser storage hold; a riser transfer station arranged within said riserstorage hold below said riser transfer opening and provided with atransfer elevator that is adapted to raise and lower a single risersection or a single riser stand in said horizontal orientation thereofso as to pass the riser section or the riser stand through the risertransfer opening; horizontal rails extending along said oppositelongitudinal sides of said riser transfer opening; and a catwalk machinehaving a mobile catwalk machine frame that is movable over saidhorizontal rails, and said catwalk machine frame having a rear end and afront end, wherein the catwalk machine frame is movable over saidhorizontal rails at least in a loading position that is above said risertransfer opening and in a riser upending position; wherein the catwalkmachine frame has two parallel and horizontal frame beams; wherein askate is supported by said frame beams and is configured to travel oversaid frame beams, wherein said skate comprises a riser end support thatis configured to support thereon a rearward end of a riser section or ofa riser stand; wherein the catwalk machine frame comprises, in additionto said riser end support, one or more additional riser support membersthat are each movable between an inactive position and an activeposition, wherein a riser section or riser stand is supportable on saidriser end support and said one or more additional riser support memberswhen in said active position thereof; and wherein the horizontal framebeams of the catwalk machine frame define between them an opening thatis dimensioned so that, with said catwalk machine frame in said loadingposition thereof and with said one or more additional riser supportmembers in said inactive position thereof, a single riser section or asingle riser stand in said horizontal orientation thereof is lowerablethrough said opening between said horizontal frame beams and into saidriser transfer opening or is liftable out of said riser transfer openingand through said opening between said horizontal frame beams.
 2. Thevessel according to claim 1, wherein said horizontal frame beams arerigidly interconnected by a transverse beam near said rear end of thecatwalk machine frame, and wherein said horizontal frame beams arefurther interconnected by one or more mobile transverse connectors thatare each movable between an inactive position, wherein a single risersection or a single riser stand in said horizontal orientation thereofis lowerable through said opening between said horizontal frame beamsand into said riser transfer opening or is liftable out of said risertransfer opening and through said opening between said horizontal framebeams, and an active position wherein said one or more mobile transverseconnector interconnect the horizontal frame beams.
 3. The vesselaccording to claim 1, wherein said horizontal frame beams are rigidlyinterconnected by a transverse beam near said rear end of the catwalkmachine frame, and wherein said horizontal frame beams are furtherinterconnected by a single mobile transverse connector arranged at thefront end of the catwalk machine frame, wherein said single mobiletransverse connector is movable between an inactive position, wherein asingle riser section or a single riser stand in said horizontalorientation thereof is lowerable through said opening between saidhorizontal frame beams and into said riser transfer opening or isliftable out of said riser transfer opening and through said openingbetween said horizontal frame beams, and an active position wherein saidsingle mobile transverse connector interconnects the horizontal framebeams.
 4. The vessel according to claim 1, wherein the vessel isprovided with one or more movable hatches which in a closed positionthereof close said elongated riser transfer opening and in an openedposition thereof open said elongated riser transfer opening.
 5. Thevessel according to claim 1, wherein the vessel is provided with a firstset of pivotal hatches, said first set of pivotal hatches being arrangedalong one of said longitudinal sides of said riser transfer opening, andwherein the vessel is provided with a second set of pivotal hatches,said second set of pivotal hatches being arranged along said other oneof said longitudinal sides of said riser transfer opening, so that withsaid pivotal hatches in a horizontal position thereof said risertransfer opening is closed and with said hatches in an upward pivotedposition thereof said riser transfer opening is open, and wherein, insaid upward pivoted position thereof, said pivotal hatches are to theoutside of the horizontal rails at a spacing that allows for travel ofthe catwalk machine frame over said horizontal rails between saidupwardly pivoted hatches.
 6. The vessel according to claim 1, whereinsaid vessel has a moonpool that extends through the hull, and whereinthe vessel is provided with a tower arranged at the moonpool and with ariser string lifting tool that is movable up and down relative to thetower, said riser string lifting tool being adapted to connect to aleading of a riser section or riser stand supported on the catwalkmachine in said riser upending position of said catwalk machine frame,said riser sting lifting tool further being adapted to support a riserstring in a firing line through the moonpool.
 7. The vessel according toclaim 1, wherein a first overhead travelling beam crane is arrangedwithin the riser storage hold, said first crane being adapted to liftand lower a single riser section or a single riser stand at leastallowing for removal of a single riser section or a single riser standriser stand from a storage rack and for placing a single riser sectionor a single riser stand into a storage rack respectively, and said firstcrane being adapted for transverse transportation of a single risersection or a single riser stand at least between said transfer stationand a position above a storage rack, wherein said first crane comprises:a travelling beam extending in a direction parallel to said storageracks and supported at each end thereof on a crane rail perpendicular tosaid storage racks, a winch trolley provided with one or more winchesand displaceable along said travelling beam, and an elongated gripperframe suspended by one or more winch driven cables from said winchtrolley, said gripper frame being provided with multiple riser grippersadapted to engage on a single riser section or a single riser stand atspaced gripping locations thereof, wherein the riser storage hold isprovided with first length storage racks adapted to store therein singlefirst length riser sections and/or pre-assembled riser stands, each ofsaid single first length riser sections or of pre-assembled riser standshaving a length of at least 100 ft. (30.48 m), wherein the riser storagehold is provided with second length storage racks adapted to storetherein single second length riser sections each having a length ofbetween 50 ft. (15.24 meters) and 90 ft. (27.43 meters), and wherein thefirst overhead travelling beam crane is adapted to transfer a secondlength riser section between each of said second length storage racksand the transfer station, and to transfer a first length riser sectionor riser stand between each of said first length storage racks and thetransfer station.
 8. The vessel according to claim 7, wherein thetransfer elevator comprises a first elevator unit and a second elevatorunit that are spaced apart in direction parallel to said storage racks,wherein each of said first and second elevator units are adapted toselectively operate stand-alone or in unison, wherein, for operatingstand-alone, each elevator unit is adapted to raise and lower a secondlength riser section, and wherein, for operating in unison, said firstand second elevator units are further adapted to raise and lower a firstlength riser section or single riser stand.
 9. The vessel according toclaim 8, wherein each elevator unit comprises a vertical guide structurestationary mounted in said storage hold, and a telescoping member whichis guided by said vertical guide structure, wherein the elevator unitfurther comprises a winch and winch driven cable connected to saidtelescoping member to cause vertical motion thereof, and wherein a risersupport member is mounted on said telescoping member and is adapted tosupport a riser section or riser stand.
 10. The vessel according toclaim 7, wherein a first group of first length storage racks is arrangedadjacent one side of the transfer station and a second group of firstlength storage racks is arranged adjacent another side of the transferstation, and wherein a first group of second length storage racks isarranged along said first group of first length storage racks andwherein a second group of second length storage racks is arranged alongsaid second group of first length storage racks.
 11. The vesselaccording to claim 7, wherein the riser storage hold is provided with asecond overhead travelling beam crane arranged within the riser storagehold, said second overhead travelling beam crane being adapted to liftand lower a single riser section or a single riser stand at leastallowing for removal of a single riser section or a single riser standriser stand from a storage rack and for placing a single riser sectionor a single riser stand into a storage rack respectively, and saidsecond overhead travelling beam crane being adapted for transversetransportation of a single riser section or a single riser stand atleast between said transfer elevator and a position above a storagerack, wherein said second overhead travelling beam crane comprises: asecond travelling beam extending in a direction parallel to said storageracks and supported at each end thereof on a crane rail perpendicular tosaid storage racks, preferably the same crane rail as the first overheadtravelling beam crane, a second winch trolley provided with one or morewinches and displaceable along said travelling beam, and possibly, anelongated gripper frame suspended by one or more winch driven cablesfrom said winch trolley, said gripper frame being provided with multipleriser grippers adapted to engage on a single riser section or a singleriser stand at spaced gripping locations thereof.
 12. The vesselaccording to claim 1, wherein the riser storage hold is provided with atleast one elongated riser workshop having a floor, preferably also wallsand a possibly also a roof, said riser workshop being arranged parallelto the storage racks and the workshop being adapted to accommodate atleast one riser section or riser stand in horizontal orientation,wherein the first overhead travelling beam crane is adapted to place ariser in the workshop and remove a riser from the workshop.
 13. A methodfor assembly of a riser string, wherein use is made of a vesselaccording to claim 1, wherein the method comprises: moving said catwalkmachine frame over said horizontal rails into said loading positionabove said riser transfer opening, bringing said one or more additionalriser support members in said inactive position thereof, lifting asingle riser section or a single riser stand in said horizontalorientation thereof out of said riser transfer opening and through saidopening between said horizontal frame beams, and bringing said one ormore additional riser support members in said inactive position thereofso as to support the single riser section or single riser stand on saidriser end support and said one or more additional riser support members.14. A catwalk machine configured for mounting on horizontal railsextending along opposed longitudinal sides of an elongated risertransfer opening onboard a vessel adapted to perform subsea wellborerelated operations involving a riser string between the subsea wellboreand the vessel, wherein the catwalk machine has a mobile catwalk machineframe that is movable over said horizontal rails, and said catwalkmachine frame having a rear end and a front end, wherein the catwalkmachine frame is movable over said horizontal rails at least in aloading position that is above said riser transfer opening and in ariser upending position, wherein the catwalk machine frame has twoparallel and horizontal frame beams, wherein a skate is supported bysaid frame beams and is configured to travel over said frame beams,wherein said skate comprises a riser end support that is configured tosupport thereon a rearward end of a riser section or of a riser stand,wherein the catwalk machine frame comprises, in addition to said riserend support, one or more additional riser support members that are eachmovable between an inactive position and an active position, wherein ariser section or riser stand is supportable on said riser end supportand said one or more additional riser support members when in saidactive position thereof, and wherein the horizontal frame beams of thecatwalk machine frame define between them an opening that is dimensionedso that, with said catwalk machine frame in said loading positionthereof and with said one or more additional riser support members insaid inactive position thereof, a single riser section or a single riserstand in a horizontal orientation thereof is lowerable through saidopening between said horizontal frame beams and into said riser transferopening or is liftable out of said riser transfer opening and throughsaid opening between said horizontal frame beams.